# Prime and composite numbers review

Review prime and composite numbers, and try some practice problems.

## What are prime numbers?

Prime numbers are numbers with exactly 2 factors.
A prime number's only factors are start color greenD, 1, end color greenD and the number start color purpleD, i, t, s, e, l, f, end color purpleD.
7 is an example of a prime number. Its only factors are start color greenD, 1, end color greenD and start color purpleD, 7, end color purpleD. It is not evenly divisible by any other whole numbers.
A factor is a whole number that can divide evenly into another number.
The factors of start color purpleD, 8, end color purpleD are: start color blueD, 1, comma, 2, comma, 4, end color blueD, comma and start color blueD, 8, end color blueD.
start color purpleD, 8, end color purpleD, divided by, start color blueD, 1, end color blueD, equals, 8
start color purpleD, 8, end color purpleD, divided by, start color blueD, 2, end color blueD, equals, 4
start color purple, 8, end color purple, divided by, start color blueD, 4, end color blueD, equals, 2
start color purpleD, 8, end color purpleD, divided by, start color blueD, 8, end color blueD, equals, 1
start color blueD, 1, comma, 2, comma, 4, end color blueD, comma and start color blueD, 8, end color blueD all divide evenly into start color purpleD, 8, end color purpleD.

## Practice set 1: Identifying prime numbers

Problem 1A
Which of these numbers is prime?
12, comma, space, 42, comma, space, 61, comma, space, 87, comma, space, 95

Want to try more problems like this? Check out this exercise.

## What are composite numbers?

Composite numbers have more than 2 factors. A composite number has factors in addition to 1 and the number i, t, s, e, l, f.
16 is an example of a composite number. The factors of 16 are 1, comma, 2, comma, 4, comma, 8 and 16, point All of these numbers divide into 16 evenly.